Method for producing an electrically conductive structure

ABSTRACT

A method produces a composite from a conductive structure, a carrier made of non-conductive carrier material made from thermosetting plastic, and at least one electronic component by laser radiation. The non-conductive carrier material having an additive, which is configured to subsequently form a catalytically active species in an electroless metallization bath by irradiation with the laser radiation. The method includes: forming the conductive structure being by irradiation using pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electroless metallization. A pulse repetition rate is set such that consecutive pulses of the pulsed laser radiation in an area of the additive to be activated or an additive area are diverted mutually overlapping onto the additive or the additive area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/DE2020/100840, filed on Oct. 1, 2020, and claims benefit to German Patent Application No. DE 10 2019 133 955.3, filed on Dec. 11, 2019. The International Application was published in German on Jun. 17, 2021, as WO 2021/115518 A1 under PCT Article 21(2).

FIELD

The present disclosure relates to a method for producing an electrically conductive structure.

BACKGROUND

In laser direct structuring (LDS), carrier materials are injection-molded into moldings in single-component injection molding using a specifically additive-enhanced plastic granulate. The additives can be converted location-selectively to catalytically active nuclei in a physical-chemical reaction by means of a laser, metal being separated at the so treated locations in a subsequent chemical metallization bath.

DE 101 32 092 A1 describes conductor track structures on an electrically non-conductive carrier material that consists of metal nuclei and a metallization subsequently deposited thereon, the metal nuclei having been produced by breaking up electrically non-conductive inorganic metal compounds that are contained very finely distributed in the carrier material by electromagnetic radiation.

DE 10 2014 114 986 A1 describes a method for producing a conductor track structure on a circuit carrier by selective laser radiation corresponding to the conductor track structures to be produced, that is subsequently produced in an electroless metallization bath. Here for example, laser radiation having a wavelength of 1,064 nanometers and a pulse frequency of 100 kHz is used.

In the case of a method for producing such an electrically conducting structure revealed in DE 10 2013 100 016 A1, the carrier material is mixed into a thermosetting copper oxide-polyester hybrid and injection-molded to form workpieces that are then location-selectively activated for a subsequent metallization by means of a laser.

Due to technological limitations, LDS methods can nowadays reliably produce track widths of no smaller than 150 μm. To further advance the desired miniaturization of MID, it is inevitable to push back this limitation further. For this purpose, great efforts are made to further focus the laser radiation and guide it more precisely across the surface of the molding.

DE 10 2012 010 635 A1 relates to a method for direct 3D structuring of hard, brittle, and optical materials where the surface is structured using an ultrashort pulse laser and thereby a 3D structure or form is specifically introduced.

SUMMARY

In an embodiment, the present disclosure provides a method that produces a composite from a conductive structure, a carrier made of non-conductive carrier material made from thermosetting plastic, and at least one electronic component by laser radiation. The non-conductive carrier material having an additive, which is configured to subsequently form a catalytically active species in an electroless metallization bath by irradiation with the laser radiation. The method includes: forming the conductive structure being by irradiation using pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electroless metallization. A pulse repetition rate is set such that consecutive pulses of the pulsed laser radiation in an area of the additive to be activated or an additive area are diverted mutually overlapping onto the additive or the additive area.

DETAILED DESCRIPTION

The present disclosure relates to a method for producing a composite from at least one conductive structure, a carrier made of non-conductive carrier material made from plastic, and at least one electronic component by means of laser radiation, wherein the non-conductive carrier material contains an additive that subsequently forms active species in an electroless metallization bath as a result of exposure to laser radiation.

In practice, in particular in the case of thermosets as carrier material, the extraneous deposition that is occurring has been found to be a disadvantage when carrying out the method for producing electrically conductive structures on or at a non-conducting carrier material by laser activation, e.g. in the case of conductor tracks. Since thermosets do not melt but are decomposed, considerable amounts of carbon are released that is catalytically active in an electroless metallization bath.

The following metallization of the metal atoms is undesirably accompanied also outside the treated area by extraneous deposition on the ablation products that are catalytically active in the metallization bath. In the case of too low a spacing of the produced conductor tracks, this extraneous deposition can in practice lead to short circuits. In the process, these ablation products turn out to be problematic also because they bond again to the plastic surface outside the structured faces on account of their high temperature during the decomposition and can therefore hardly be removed. With increased miniaturization of the structures to be produced, these problems arise not only with thermosets but in principle also with all plastics.

When the temperature is too high during structuring, the ablation products become so hot that they firmly adhere to the surface of the carrier material that can then no longer be cleaned reliably. The adhering, catalytically active ablation products lead in particular in the area of recesses to “collar formation” by extraneous deposition in the edge area of the recesses. Although practice has shown that this effect can be minimized by a significant reduction of the laser power, however a markedly longer cycle time results.

The present disclosure provides a method where an adverse impact of the conductive structure so produced on the carrier material on account of ablation products is markedly reduced. According to the present disclosure, a further reduction of the structure variables of the electrically conductive structures is to be made possible.

Aspects of the present disclosure provide a method for producing a composite from at least one conductive structure, a carrier made of non-conductive carrier material made from thermosetting plastic, and at least one electronic component by means of laser radiation, the non-conductive carrier material containing an additive, that subsequently forms catalytically active species in an electroless metallization bath by irradiation with the laser radiation, the conductive structure is formed by irradiation by means of pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electroless metallization and the pulse repetition rate is set such that consecutive pulses in the area of an additive to be activated in each case or an additive area are diverted mutually overlapping onto the additive or the additive area.

Aspects of the present disclosure are based on the surprising finding that the method for producing an electrically conductive structure by laser activation of the metal compounds contained in the additive, in particular using ultrashort pulse lasers, can be applied without any problems, in particular also in the case of thermosets, and at the same time has the advantage that less extraneous deposition occurs.

This for the first time creates a method for laser direct structuring that, on the one hand, reliably achieves the energy input required for laser activation, but on the other hand limits the temperature increase such that, not only considerably fewer ablation products arise, but also their temperature is so low that also the adhesion to the carrier material is very low and they therefore can be removed easily.

According to the aspects of the present disclosure, it is therefore possible to produce particularly fine electrically conductive structures because avoiding extraneous deposition also prevents the risk of associated short circuits. As a result, the structure width and the spacing of the structures can be reduced.

A further particularly promising development of the method according to the present disclosure is also achieved by dimensioning the number of laser pulses per second (pulse repetition rate) to be so high, for example 2 to 2.5 MHz, that consecutive pulses act in the area of an additive particle to be activated in each case or of an additive area with mutually overlapping exposure areas. Therefore, always a plurality of consecutive pulses acts on each additive particle or on each additive area, the energy input being correspondingly increased as a result.

This achieves a precise temperature management that rules out that the introduction of thermal energy into the carrier material is so low that the temperature is not sufficient for reducing the additive, for example a Cu—Cr spinel to form elemental copper, and thus, the catalytically active species are not produced or not produced reliably for the desired metallization and in particular irregular partial metallizations occur. The overlapping exposure faces of consecutive pulses also ensure that the temperature during structuring is not too high so that in contrast to the prior art the ablation products do not become hot and therefore cannot undesirably adhere to the carrier material such that they can no longer be reliably removed.

The method produces a composite where the non-conductive carrier material contains an additive that exhibits catalytically active species formed as a result of exposure to laser radiation, the conductive structure being formed by irradiation by means of pulsed laser radiation, in particular an ultrashort pulse laser, and by a subsequent metallization in the metallization bath. According to an aspect of the present disclosure, use of pulsed laser radiation achieves a quasi athermal treatment of the carrier material when the parameters are chosen appropriately, in that the material is directly evaporated on account of the enormously high peak intensities, so that no or almost no melt is created. Here, the pulses are so short that during the pulse duration there is no transfer of the energy into lattice vibrations and therefore no temperature increase. It is assumed that the energy input by the ultrashort pulse corresponds to the energy required for evaporating the material so that no further energy remains for a thermalization.

Contrary to the prejudice of experts that previously assumed that the activation of the metal compounds and the formation of catalytically active nuclei in the areas thus laser-activated, correspond to a thermal process that requires high temperatures for breaking up the additive particles, an aspect of the present disclosure is based on the surprising finding that the basis is not the thermal energy input, but the maximum intensity, which in the process creates the cause and the required prerequisite for the activation of the metal compounds.

It turns out to be particularly advantageous for the non-conductive carrier material to contain an inorganic filler having a maximum particle size of 50 μm. Because of this, also such filler materials can be used that cannot be destroyed or decomposed by the impacting laser radiation, because on account of their low particle size they cannot impair or hinder subsequent treatment methods, for example introducing recesses such as drill holes including vias or blind holes. The fillers can therefore be selected without any limitation corresponding to the desired technical properties of the thermoset, for example with a view to viscosity, CTE (Coefficient of Thermal Expansion) or the solidification time.

In this way, the adhering catalytically active ablation products that are particularly disadvantageous in particular in the prior art, are reliably avoided in the area of holes as so-called “collar formation”. According to the present disclosure, this does not increase the cycle time. Using ultrashort pulse lasers of a picosecond laser source produces considerably less heat during the ablation. When drilling, this prevents the formation of hot ablation products and the collar formation even in the case of higher powers. Using higher powers leads to greater removal rates, and this can reduce in practice the cycle time even more.

The parameters remaining the same during structuring of the carrier material and the heat input being reduced thereby, which could lead to insufficient activation of the additive, the change from nanosecond to picosecond pulses is particularly advantageously compensated by an overlapping area of the individual pulses, this being made possible by using high pulse repetition rates, for example in the range between 2 and 2.5 MHz.

Another, likewise particularly promising development is achieved in that by using a non-contacting measuring method, in particular by using electromagnetic radiation such as X-rays, the position and/or orientation of at least one electronic component in the carrier material and subsequently a deviation from the actual position and/or the actual orientation from the desired position and/or desired orientation is determined and correction values are derived therefrom for the subsequent irradiation of the carrier material by means of the pulsed laser radiation and subsequently irradiation is carried out taking into account these correction values. As a result, the individual positional deviation of the electronic component from the desired position is determined in particular when embedding one or more electronic components into a compound. For this purpose, for example by means of an X-ray method, the precise position and torsion of the electronic component is determined and the irradiation of the activatable additives or the catalytically active species is carried out taking into account the correction values. By means of software, the conductor tracks and holes to be structured can in this way be matched to an actual position and orientation of the electronic component in the carrier material, thus avoiding rejects and increasing the reliability considerably.

When, according to a preferred development, the size and/or mass of the individual filler particles contained in the carrier material is considerably larger than the size and/or mass of the individual additive particles contained in the carrier material, the size or mass differences of the filler particles on the one hand and the additive particles on the other hand surprisingly leads to an inhomogeneous distribution of the additive and filler particles with the result that during the course of the treatment of the carrier material, the relatively large or heavy filler particles primarily accumulate on the inside or in the medial area of the carrier material, while in contrast the comparatively small or light additive particles are displaced into the layers close to the edge of the carrier material. The concentration of the additive in the layers close to the edge increasing in this way, the activation process there can be considerably improved, it thereby being possible to carry it out even with reduced radiation intensity without having to increase the total amount of the added additives for this purpose. The thus reduced proportion of additives in the core of the carrier material at the same time avoids unwanted changes of other material properties.

For example, 3 to 15 percent by weight, preferably 6 to 12 percent by weight, of an LDS additive are contained in the carrier material.

While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 

1. A method for producing a composite from at least one conductive structure, a carrier made of non-conductive carrier material made from thermosetting plastic, and at least one electronic component by laser radiation, the non-conductive carrier material comprising an additive, which is configured to subsequently form a catalytically active species in an electroless metallization bath by irradiation with the laser radiation, the method comprising: forming the conductive structure being by irradiation using pulsed laser radiation having a pulse duration of less than 100 picoseconds and subsequent electroless metallization, a pulse repetition rate being set such that consecutive pulses of the pulsed laser radiation in an area of the additive to be activated or an additive area are diverted mutually overlapping onto the additive or the additive area.
 2. The method of claim 1, wherein the laser radiation is imaged through a part-transmissive mask onto the carrier.
 3. The method of claim 1, wherein a polygon scanner is used for positioning the laser radiation on the carrier.
 4. The method of claim 1, wherein a plurality of galvanometer scanners are used for positioning the laser radiation on the carrier.
 5. The method of claim 1, wherein a resonant mirror is used for positioning the laser radiation on the carrier.
 6. The method of claim 1, wherein by using a non-contacting measuring method, an actual position and/or an actual orientation of the electronic component in the non-conductive carrier material and subsequently a deviation from the actual position and/or the actual orientation from the desired position and/or desired orientation is determined,. and correction values are derived therefrom for the subsequent irradiation of the non-conductive carrier material by the pulsed laser radiation, and irradiation is carried out taking into account the correction values.
 7. The method of claim 1, wherein four galvanometer scanners are used for positioning the laser radiation on the carrier.
 8. The method of claim 6, wherein by using the non-contacting measuring method comprises using X-rays. 